Light emitting devices such as light emitting diodes (LEDs) and laser diodes (LDs) are well known solid state lighting elements capable of generating light upon application of a sufficient voltage. These light emitting devices are commonly used in various lighting and illuminating applications such as general lighting, automotive lighting, displays, and projection applications.
It is often desirable to incorporate phosphor into these light emitting devices to enhance the emitted radiation in a particular wavelength region and/or to convert at least some of radiation to another wavelength region. Generally, white light can be generated with blue-emitting devices and one or more of yellow, red, and green emitting phosphors. For example, red-emitting phosphors based on complex fluoride materials activated by manganese (Mn4+), such as those described in U.S. Pat. Nos. 7,358,542, 7,497,973, and 7,648,649, can be utilized in combination with yellow/green emitting phosphors such as YAG:Ce or other garnet compositions with a blue-emitting device, to achieve warm white light (CCTs<5000 K on the blackbody locus, color rendering index (CRI>80).
Typically, phosphor materials in particulate form are dispersed in a resin such as silicone to form a layer for use in lighting devices. However, such conventional phosphor materials (in layers) may exhibit low thermal conductivities and thermal quenching (a decrease in internal quantum efficiency with temperature). It has been challenging using conventional phosphor materials in high power density lighting devices because the phosphor materials may deteriorate and damage (for example, decompose) under high power density light. For example, as the power density of excitation light increases, the heat generated by the device increases that is detrimental for the phosphor materials. The use of conventional phosphor materials in such high power density lighting devices limits the applicable device power and performance.
Therefore, there remains a need for phosphor materials that facilitate the manufacturing of high power density lighting devices that include phosphor materials, and provide improved performance.